The protection of stone in historic buildings with fluoropolyethers is known. The use of neutral fluoropolyethers for such protection is described in U.S. Pat. No. 4,499,146 to Piacenti et al.; the use of fluoropolyethers that have at least on anchoring group bound thereto is described in U.S. Pat. No. 4,745,009 to Piacenti et al., U.S. Pat. No. 4,746,550 to Strepparola et al., and U.S. Pat. No. 4,902,538 to Piacenti et al. Unfortunately, such techniques rely on environmentally deleterious solvents such as chlorofluorocarbons. Because of the extremely large volumes of compositions required to protect such civil infrastructure, the use of compositions that contain environmentally undesireable solvents is a severe problem.
Carbon dioxide has been used as a solvent for some fluoropolymers (see, e.g., U.S. Pat. No. 5,496,901 to DeSimone). V. Krukonis and M. McHugh, Supercritical Fluid Extraction, 156-158, describe the fractionation of a perfluoroalkylpolyether oil and a chlorotrifluoroethylene oligomer in supercritical carbon dioxide. None of this literature suggests methods of protecting civil infrastructure with such materials.
U.S. Pat. No. 5,211,342 to Hoy et al. describes electrostatic liquid coating application processes in which supercritical fluids such as carbon dioxide are used to coat substrates with various polymers. Civil infrastructure substrates are neither suggested nor disclosed, and fluoropolyether polymers are neither suggested nor disclosed. In addition, while electrostatic spraying techniques are useful for circuit boards and other small substrates, they are less desireable for the treatment of civil infrastructure substrates.
U.S. Pat. No. 4,923,720 to Lee et al. describes supercritical fluids such as carbon dioxide as diluents for the application of viscious coatings, but does not suggest such coatings for civil infrastructure.
In view of the foregoing, there is a continued need for new techniques for treating civil infrastructure substrates to protect them from the damaging effects of pollution, weather, noxious fumes and the like.